Tuesday, November 13, 2012

BALD EAGLE - HERO OR VILLAIN?

The Bald Eagle is the national symbol of the United States
of America. It seems appropriate for a country to have such a majestic bird as a
symbol. Long-lived, monogamous, good parent, characteristic of wild places,
Bald Eagles excite awe and admiration wherever they fly.

There have been notable dissenters from this view, including
Ben Franklin, in a letter to his daughter 20 June 1782: "For my own part I
wish the Bald Eagle had not been chosen the Representative of our Country. He
is a Bird of bad moral Character. He does not get his Living honestly. You may
have seen him perched on some dead Tree near the River, where, too lazy to fish
for himself, he watches the Labour of the Fishing Hawk; and when that diligent
Bird has at length taken a Fish, and is bearing it to his Nest for the Support
of his Mate and young Ones, the Bald Eagle pursues him and takes it from
him."

Yes, Bald Eagles are inveterate kleptoparasites, robbing Ospreys and other
raptors of their prey. Like all birds, they have terrific vision and are aware
of what goes on all around them, even at some distance. Not even a swift and
strong Peregrine Falcon can withstand the attack of an eagle determined to
wrest a recently captured bird from it.

In the middle of the 20th Century, Bald Eagle populations
were decimated by ingesting DDT along with the fish and fish-eating birds that
they preyed on. DDT compromises calcium transport, and the eggs laid by the
eagles, with inadequate calcium, were thin-shelled enough to crack under the
weight of an incubating female. Reproductive success fell and populations
declined along with it.

DDT was banned in the US in 1972, and eagle populations have
been rebounding ever since, to levels greater than any previously documented.
Their numbers have skyrocketed in particular in the Pacific Northwest, which
must be optimal eagle country.

Unfortunately, the consequences of this are dire for some
other bird species. Eagles are opportunists above all, and they have learned to
make a living, at least in spring and summer, by hanging around bird colonies.
With present eagle numbers, colonies of Great Blue Herons, Caspian Terns, and
Common Murres on and near the coasts have been hit hard by these predators, sometimes
just single birds taking advantage of the prey concentration.

The nesting birds have no way to withstand eagle predation, losing eggs, young
and even adults to the predators. Even though eagles may eat a small percentage
of the birds in a colony, their presence causes nesting to be disrupted to the
point of complete colony abandonment. Because of this, numerous Great Blue
Heron colonies have failed, and even huge colonies of thousands of murres and
terns have been abandoned.

In the coming years, wildlife managers will have to figure
out how to deal with this dilemma. Bald Eagles are not on the endangered species
list any more, but they are still protected. The birds whose colonies they are
destroying are also protected and of concern, and what should we do when one valued
species affects another one so severely?

1 comment:

Anonymous
said...

No action will ever be taken to limit populations of Bald Eagles. Just like Wild Horses (which have become a major pest in the midwest) Bald Eagles are too closely attached to Americans' emotions being the national animal to represent the US and all..

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About the Slater Museum

Our goals are to preserve and provide a collection of specimens to be used for research and education. Located in Tacoma, Washington, the Slater Museum is one of the region's significant repositories for bird, mammal, reptile, amphibian and plant specimens from the Pacific Northwest. In addition, we strive to educate the local community about nature and about the value of museums.